bug: handling of prefixed properties is inconsistent

[kristerkari]

This should be allowed, but gives a warning:

.foo {
  transition-property: -webkit-transform;
}

This does not give a warning:

.foo {
  transition: -webkit-transform 2ms linear;
}

This should be allowed, but gives a warning:

.foo {
  transition-property: -webkit-text-stroke-color;
}

This does not give a warning:

.foo {
   transition: -webkit-text-stroke-color 2ms linear;
}

/ping @konstantin24121